1. Field of the Invention
This invention relates to the field of cement compositions and more specifically to the field of cement compositions comprising carboxylated inulin, for example carboxymethylated inulin, as well as methods for using such compositions to cement a workspace such as a wellbore.
2. Background of the Invention
A natural resource such as oil or gas residing in a subterranean formation can be recovered by drilling a well into the formation. The subterranean formation is usually isolated from other formations using a technique known as well cementing. In particular, a wellbore is typically drilled down to the subterranean formation while circulating a drilling fluid through the wellbore. After the drilling is terminated, a string of pipe, e.g., casing, is run in the wellbore. Primary cementing is then usually performed whereby a cement slurry is pumped down through the string of pipe and into the annulus between the string of pipe and the walls of the wellbore to allow the cement slurry to set into an impermeable cement column and thereby seal the annulus. Secondary cementing operations may also be performed after the primary cementing operation. One example of a secondary cementing operation is squeeze cementing whereby a cement slurry is forced under pressure to areas of lost integrity in the annulus to seal off those areas.
The typical cement compositions include various components that are mixed together to form a cement slurry. The resulting reaction from the mixture of the components is fast such that the cement composition may set very rapidly, e.g., within a few minutes at room temperature and pressure. The rate of reaction further increases as the temperature increases. As such, the thickening times of the compositions may be unacceptably short to allow them to be pumped to their desired downhole locations, which make the use of such compositions in well cementing a challenge. As a result, the cement slurry may set inside the casing, which may cause expensive drill out operations.
Retardants have typically been used to lengthen the thickening time of the cement and thereby delay setting of the cement until after placement. Typical retardants include lignosulfonates such as HR-5 available from Halliburton Energy Services of Duncan, Okla., synthetic copolymers such as SCR-100 and SCR-500 available from Halliburton Energy Services, and the like. Drawbacks to using typical retardants include environmental concerns such as poor biodegradability of the retardants. To address environmental concerns, carboxymethylated cellulose (e.g., carboxymethylhydroxyethylcellulose), which is a biodegradable material, has been used in the past as a retardant in cement compositions. Drawbacks encountered with carboxymethylated cellulose include very high surface slurry viscosities, particularly when higher quantities of the retarder are used to provide retardation for cementing high temperature zones. Other drawbacks to using carboxymethylated cellulose include a decrease in slurry viscosity due to thermal thinning as the slurry temperature increases to wellbore temperature during pumping and placement behind the casing, which may result in potential particle settling. Dispersants and suspension aids are thereby typically used with carboxymethylated cellulose in the cement composition. Additional drawbacks to using carboxymethylated cellulose include treating the cellulose, i.e. hydroxyethylation, to provide water solubility, for example as in the preparation of carboxymethylhydroxyethylcellulose.
Consequently, there is a need for a more effective biodegradable retardant for cement compositions. Further needs include a biodegradable retardant that maintains suspension in cement compositions at high temperatures. Additional needs include a biodegradable retardant that is soluble in water.